Tuned transformer



June 1o, 1930. C, J, ,.-lTCH 1,762,221

TUNED TRANSFORMER Filed Nov. 28, 1924 2 Sheets-Sheet 1 June l0, 1930. c. J. FITCH 1,762,221

TUNED TRANSFORMER Filed Nov. 28, 1924 2 Sheets-Sheet 2 I 0.0m V Y V INVENTOR l K il Patented ...lune 10, 1930 PATENT y OFFICE NITED STATES CLYDE J'. FITCH,` OE'BBOOKLYN, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

RADIO CORPORATION OF AMERICA, 0F NEW YORK, N. Y., A .CORPORATION 0F DELA- WARE .TUNED 'rnANsroRMER Application filedy November 28, 1924. Serial No. 752,623.v

This invention relates particularly to long wave radiofrequency amplifiers of the type known as intermediate amplifiers employed One of the principal objects of this invenvtion is to provide a transformer for use in cascade audion 'amplifiers that may be readily adjusted to respond with maximum efiiciency at a predetermined narrow band of frequencies and which will thus enable each transformer of an intermediate amplifier being adjusted to respond with maximum efficiency under lthe conditions in which it is operating at the frequency which it is de` sired to amplify and thus provide that the amplifier as-awhole .will operate with maxi-v mum 'eilicienc'y at the` desired frequency.

Other import-'ant features of the invention and the novel features of. construction and relation of parts bywhich tlie objects are attained will appear from the following specification.

In the drawings accompanying and forming part of this specification, the invention is illustrated embodied in only one lof* its practical forms, wherein: i

Figure 1 isa perspective view of the complete transformer.

Figure 2 is a plan view of the transformer assembly with the tuning condenser removed.

Figure 3 is a cross sectional view of condenser and transformer-partstaken'on substantially the plane of li-ne 3-3 of Figure 2.

Figure 4 is a wiring diagram illustrating use of the invention in an intermediate amplier.

`The device consists in the present disclosure of a transformer section 5 and a superposed condenser section 6 mechanically cou-v pled in this relation by through bolts 7.

The transformer shownin Figures 2 and 3 as consisting of a primary winding 8 and a secondary winding 9 mounted in spaced relation on a core 10-1nade up of thin iron laminations. This transformer is supported and positioned by a strip 11 of wood or other suitable supporting material through which the core is passed and which is disposed in the space between the two transformer windings. This support is shown in Figure 2- as of a length to lit diagonally'in the chamber provided in the bottom of the unit by the substantially rectangular casing 12 which is closed at the bottom b v the cover 13 and atthetop by the base l-l of the condenser.

The terminals 15. 16 and 1T, 1S ofthe transformer primary and secondary respectively are mounted on the front wall of this casing and connected with the two windings bv suitable leads 19. 20, and :21.22. insulating chamber containing the transformer may be filled with suitable insulating compound which as it hardens will secure the parts in the relation shown and with the connections properly spaced.

The transformerconstructed and mounted as shown forms a very compact unit and this.

desirable feature of compactness is carried out further by making the condenserof two plates 23, 24, opposed to each other on the lbase 14, the second plate being of bowed conformation and vadapted to be forced toward the first, -against an interposed layer $25 of mica. or otherl suitable dielectric by a screw stud 26 engaged with a nut 2T held non-rotatably by lugs 28 struck up from the bowed plate.

The condenser plates are enclosed within a hollow cover 29 forming the upper portion and top of the instrument. the operating screw b'eing journaled in this top at 30 and provided with an external operating knob or dial`31.' I

In Figure 3 the lower condenser plate 23 is shown as held by the through screws 7 at the left and the upper plate 24 is shown as held by the right hand pair of through screws, the nuts 32 and 33 on these respective n' desa-d, the

screws being turned down onthe condenser plates so as to clamp the parts together. This construction at tliesame time brings the condenser plates into electrical contact with the screws mentioned and this fact is made ilse of by mounting the condenser terminals 34, 35 on those-screws at the under side of the condenser base, where they are connected across the secondary of the transformer by short leads 36, 37 secured at the inside of the case to the secondary terminals 17, 18. Nuts 38 on the upperends of the through screws serve to secure the top in place. It will be evident that this through Screw construction provides an inexpensive and at the same time very practical method of mounting and 'securing the condenser and transformer parts in superposed relation and also provides for the quick and easy assemblage of these parts.

The instrument thus constructed is of relatively small size and substantially rectangu- ,lar form so that it will fit in small spaces and be set as. close as desirable to other instrumentalities. Theterminals being all located at the forward lower portion of the apparatus, may be connected with .the tube sockets by short simple leads and the control knob being on the top of the instrument, provides for its ready adjustment afterall the parts are assembled and the set is therefore in shape for balancing the condensers.

In Figure 4, four of these tuned transformers are indicated at A, B, C, D in use as a long wave intermediate amplifier. Necessarily, in such a relation, the capacities and inductive values of the connections used, the vacuum tubes and other elements will vary, but this invention makes it possible,r after all the parts have been mounted and-connected in their final relation, to Ytune each transfoinier individually in its own particular situationlto operate -at maximum eiicieiicy at the frequency which it is desired to aniplify. One method for the accomplishment of this result is toA first set all the condenser dials at some arbitrary point, say at the fifty degree' or half-Way mark, and then tune in a station with the tuning and oscillator conti'ols of the receiving set so that the carrier wave will be heterodyned to the lower frequeiicy and amplified by lthe transformer coupled amplifier; then eachv transformer,` in turn, is tuned by means of its condenser until the station signal is brought to a maximum.'

This tuning of each transformer to the maximuni effect makes certain that each transformer is tuned to the same wave length and that the amplifier as a whole will therefore operate at maximum efficiency.

This operation at maximum eiiiciency, in addition to strengthening. the signals materially, increases the selectiveness of a receiving set. Once the transformers are tuned to suit their particular surroundings and cooperating parts, they need not be tunedl again unless possibly it be found desirable to re-tune when different vacuum tubes are used or when 'some of the connections are changed. Thus, after the transformers are individually tuned, they willordinarily be left at such adjustments, the tuning of the set for receiving different stations being effected in the usual way by adjustment of the tuner and oscillator circuits.

What is claimed is:

1. In a device of the character disclosed, a case, a transformer mounted in said case, an insulating base mounted on said case, a hollow cover engaged over said base, condenser elements on said base within k said hollow cover, condenser adjusting means projecting up through the hollow cover, through fastenings for securing the cover, base and case together, condenser terminals associated with certain of said through fastenings and transformer terminals on the case connected with said condenser terminals.

2. In a device of the class described, a closed casing comprising an upper section, a lower section and a partition separating said sections, a transformer mounted in the lower section, through bolts securing said casing sections, condenser plates having apertures through which said bolts extend, control 9 means exterior of said casing connected to one of said condenser plates to vary the effective distance between said condenser plates and 'connections between said condenser plates and the transformer secondary.

3. In combinatlon, an insulating case, a

i transformer disposed within the latter, an insulating cover for said case, metallic means 'for securing the cover to the case, condenser plates mounted on said cover, said plates being-affixed to the latter by the metallic means, an insulating closure disposed over the plates and engaging the cover thereby enclosing the plates and electrical connections from the metallic means to the transformer.

4. In. combination, an insulating casing provided with an open top, a transformer disposedwithin the casing, a second insulating casing provided with a closed top and bottom, metallic means for securing the bottom of thel second casing in position on the open top of the first casing to cover the same, a book type condenser disposed within said second casing and having its plates secured to the bottom of said second casing by said metallic securing means, and connections from the metallic securing means to the transformer secondary.

In witness whereof, I have hereunto set my hand this 3rd day of November, 1924:.

i CLYDE J. FITCH. 

